When using a ladder to scale a building, it is quite important to position the ladder securely so that the ladder does not move or fall resulting in injury to the user. It is for this reason that commercial construction which is regulated by the Occupational Safety and Health Administration (OSHA) requires that the upper end of the ladder be secured to the building against which it is rested. While there have been previous attempts to develop ladder retaining devices, as shown in U.S. Pat. Nos. 1,374,060, 1,982,572, 3,853,202 and 4,444,291, there remains a definite need for a simple, reliable retaining device to secure a ladder to a building, particularly, flat top commercial buildings having parapet walls and no external guarders.